In recent years, recording devices have continually grown in recoding capacity, and research and development are under way for realizing a device including a magnetic disk drive that has a record density exceeding 1 T bit per an area of 2.54 cm×2.54 cm (one inch square). Increasing the record density of the recording medium requires a reduction of the volume of magnetic grain composing the magnetic disk medium. Now, the magnetic grain volume is represented by V, and a magnetic energy of the grain is represented by KuV, in which “Ku” of the grain represents a magnetic anisotropic energy density. When V is reduced to improve the record density, the energy KuV is reduced, whereby a problem of thermal fluctuation is actualized in that the record information is altered due to thermal energy of about the room temperature. Generally, in order to prevent the problem of thermal fluctuation, a method of utilizing a magnetic grain having a large value of the density Ku. Generally, however, increasing the density Ku involves a proportional increase of a coercive force Hc of the magnetic grain, thereby resulting in an increase of a magnetic field strength necessary for writing (including overwriting) of magnetic information onto the magnetic disk medium. The magnetic disk drive causes a recording head, which is provided in the disk drive, to generate a magnetic field, thereby writes magnetic information. In this case, however, since the magnitude of a magnetic field strength generatable by the recording head is limited, a problem arises in that an increase in the coercive force Hc disables writing of the magnetic information.
To overcome such problems, a heat-assisted magnetic recording system has been proposed. According to the system, a magnetic grain having properties of reducing the coercive force Hc in association with the temperature increase is used. In the event of overwriting magnetic information, an overwrite- or rewrite-desired part of magnetic grain is heated by using evanescent light and Hc is temporarily reduced, thereby to write through the recording head.
A heat-assisted magnetic disk drive using a heat-assisted magnetic recording scheme includes a spindle and pivot mounted to a housing, a magnetic disk fixed to a rotational spindle, a head assembly movable on the pivot at one degree of freedom, a suspension fixed to the head assembly, a light emitting portion for emitting light, a head slider supported by a suspension, a recording head buried in a surface on a magnetic disk side of a head slider, a light receiving area (“slider light receiving area,” herebelow) buried in a sidewall of the head slider, an optical waveguide buried in the head slider, and a light irradiating portion provided in the vicinity of the recording head to irradiate light onto a magnetic disk. When writing information, the magnetic field is generated by using the recording head, light is emitted from the light emitting portion. Then, the light is propagated on the slider light receiving area, and is irradiated onto the magnetic disk from the photo-injection portion from the light irradiating portion through the optical waveguide. In this manner, a process of heating the magnetic disk is performed (refer to Non-patent Publication 1 (*1) listed below).
However, the magnetic disk medium surface has alteration or deformation (“runout”) along an axial direction of the spindle in association with, for example, the shape of the medium surface or distortion in the event of fixing of the medium to the spindle. The head slider followingly moves along the axial direction of the spindle in synchronism with the runout in a slightly lifted state from the medium surface due to the air bearing membrane effects. Further, there is a magnetic disk drive that has a configuration in which a head portion deflects relative to a slider portion in order to achieve a further fly height reduction of the slider. The light emitting portion for emitting heat assisted magnetic recording light is fixed to an external portion of the head slider. As such, the following-motion of the head slider or the like causes variation in relative positions of the light emitting portion and the spindle axis direction of the slider light receiving area existing on the head slider, that is, along the direction perpendicular to the medium surface.
The head slider and the light emitting portion are rotatable with respect to a plane parallel to the medium. For this reason, deflection can be caused in the relative positions of the light emitting portion and slider light receiving area along the direction parallel to the medium surface either passively due to the influence of the runout or positively due to activation of a micro-actuator provided to make fine adjustment of a position on the magnetic disk.
Because of the relative position variation along any one of the directions, the amount of light incident in the event of magnetic information writing is not fixed to a constant amount, and the amount of light irradiated onto the magnetic disk from the light injecting portion of the head slider is reduced. In this case, the amount of heat for reducing the coercive force Hc becomes insufficient, so that writing of the magnetic information is disabled—which leads to a recording error.
In order to prevent the problem of the recording error caused due to the head-slider attitudinal variation of the head slider, the amount of head-slider attitudinal variation has to be measured.
A measuring method for the amount of head-slider attitudinal variation has been proposed as disclosed in Patent Publication (*2) listed below, and a measuring method for the amount of head-slider positional variation has been proposed as disclosed in Patent Publication (*3) listed below.
(*1) Non-patent Publication 1: Ed Gage, et al, “Integration Challenges for Heat Assisted Magnetic Recording”, IDEMA JAPAN International Disk Forum 2006, Jun. 9, 2006
(*2) Patent Publication 1: Japanese Unexamined Patent Application Publication No. 2002-245742
(*3) Patent Publication 2: Japanese Unexamined Patent Application Publication No. 2004-14092